:root{--bg: #0b1220;--bg-elevated: #121a2b;--bg-card: #162033;--border: rgba(120, 160, 220, .18);--text: #e8eef8;--muted: #93a4c3;--accent: #3b82f6;--accent-soft: rgba(59, 130, 246, .18);--danger: #ef4444;--font-sans: "DM Sans", system-ui, sans-serif;--font-display: "Fraunces", Georgia, serif;color-scheme:dark}*{box-sizing:border-box}html,body,#root{min-height:100%}body{margin:0;font-family:var(--font-sans);color:var(--text);background:radial-gradient(1200px 600px at 10% -10%,rgba(59,130,246,.22),transparent 55%),radial-gradient(900px 500px at 90% 0%,rgba(14,165,233,.12),transparent 50%),linear-gradient(180deg,#0b1220,#0a101c)}a{color:inherit;text-decoration:none}button,input{font:inherit}.shell{width:min(1120px,calc(100% - 48px));margin:0 auto;padding:32px 0 64px}.brand{font-family:var(--font-display);font-size:1.75rem;letter-spacing:-.02em}.muted{color:var(--muted)}.card{background:color-mix(in srgb,var(--bg-card) 88%,transparent);border:1px solid var(--border);border-radius:18px;padding:24px;-webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px)}.grid-courses{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:16px}.btn{-webkit-appearance:none;-moz-appearance:none;appearance:none;border:0;border-radius:12px;padding:12px 16px;background:var(--accent);color:#fff;font-weight:600;cursor:pointer}.btn:disabled{opacity:.6;cursor:not-allowed}.btn.ghost{background:var(--accent-soft);color:#dbeafe}.field{display:grid;gap:8px;margin-bottom:14px}.field input{width:100%;border-radius:12px;border:1px solid var(--border);background:var(--bg-elevated);color:var(--text);padding:12px 14px}.error{color:#fecaca;background:#ef44441f;border:1px solid rgba(239,68,68,.35);border-radius:12px;padding:10px 12px;margin-bottom:12px}.topbar{display:flex;align-items:center;justify-content:space-between;gap:16px;margin-bottom:28px}.study-layout{display:grid;grid-template-columns:1.2fr 1fr;gap:20px}@media(max-width:900px){.study-layout{grid-template-columns:1fr}}.video-frame{aspect-ratio:16 / 9;border-radius:16px;border:1px solid var(--border);background:linear-gradient(180deg,#1e3a8a59,#0f172ae6),#0f172a;display:grid;place-items:center;color:var(--muted);overflow:hidden}.video-frame video{width:100%;height:100%;object-fit:cover}.tabs{display:flex;gap:8px;margin:14px 0}.tab{padding:8px 12px;border-radius:999px;border:1px solid transparent;color:var(--muted);background:transparent;cursor:pointer}.tab.active{color:#dbeafe;background:var(--accent-soft);border-color:#3b82f659}.cue{border:1px solid var(--border);border-radius:14px;padding:14px;margin-bottom:10px;background:#0f172a8c}.cue.active{border-color:#3b82f6b3;box-shadow:0 0 0 1px #3b82f640}.cue .en{font-size:1.05rem;line-height:1.5}.cue .zh{margin-top:6px;color:var(--muted)}.auth-wrap{min-height:100vh;display:grid;place-items:center;padding:24px}.auth-card{width:min(420px,100%)}.controls{display:flex;align-items:center;justify-content:center;gap:10px;margin-top:18px;flex-wrap:wrap}.chip{border:1px solid var(--border);background:#0f172aa6;color:var(--muted);border-radius:12px;padding:10px 12px;cursor:pointer}.chip.on{color:#dbeafe;background:var(--accent-soft);border-color:#3b82f673}.play{width:64px;height:64px;border-radius:999px;border:0;background:var(--accent);color:#fff;font-weight:700;cursor:pointer;box-shadow:0 10px 30px #2563eb59}